The disclosed subject matter relates generally to techniques for lens-free super-resolution imaging.
The field of optical microscopy includes systems with imaging optics, e.g., series of lenses that project an object plane onto an imaging-plane which, in turn, is typically recorded by an imaging array such as a CCD camera or the retina. However, in some applications, it can desirable to acquire an image without the use of lenses. For example, limited-space applications such as endoscopy can benefit from small, lens-free imaging systems.
Electromagnetic waves, including those in the infrared, visual, and ultraviolet spectrum, propagating through a medium can undergo frequency-dependent effects known as dispersion. For example, light traveling through a prism can undergo phase velocity dispersion, wherein different frequencies of light are refracted differently (i.e., different wavelengths have different propagation velocities). The “dispersion relation” can describe the relation of wave properties, such as for example wavelength, frequency, velocity, and refractive index of a medium. Dispersion relations can depend on material composition of a medium through which an electromagnetic wave travels, the geometry of the medium, and other factors.
Photonic crystals (PCs) can have peculiar optical properties, which can allow for the modification and engineering of the dispersion relation of the crystal for photons at optical frequencies. Photonic crystals can be fabricated to affect the motion of photons. For example, nanoscale waveguides can be created by introducing defects in a periodic structure. Optical cavities can be created by removing one or more holes in a PC lattice. Such cavities can be high-Q and can have desirable modal volume. Additionally, optical cavities can be designed to include more than one mode localized in the cavity area. Such modes can be referred to as standing wave modes, which can be composed of superpositions of forward and backward traveling Bloch modes. Each standing wave can have a unique spatial distribution, which can correspond to a different resonant frequency for each mode.